1. Field of the Invention
This invention relates to a shunt trip mechanism for a circuit interrupting device, and more specifically relates to a simple, reliable, inexpensive and reusable shunt trip mechanism for a bus-mountable, manually resettable circuit interrupting device, the shunt trip mechanism being at ground potential and being manually resettable.
2. Prior Art
An improved operating mechanism for a circuit interrupting device is disclosed and claimed in co-pending, commonly assigned U.S. patent application, Ser. No. 930,774, filed 8-3-78 in the name of Opfer and Vojta, and entitled, "Operating Mechanism for a Circuit Interrupting Device." Such co-pending, commonly assigned, U.S. patent application, is specifically incorporated by reference hereinto.
The above-referred to patent application discloses an operating mechanism of the type which renders a circuit interrupting device inexpensive and simple even though its interrupting capabilities are more limited than exotic, broad-range devices, such as circuit breakers, reclosers, and circuit switchers. Moreover, although more expensive than fuses, the circuit interrupting device with the operating mechanism of that patent application is reusable and is resettable from ground level and includes "intelligence" which senses the condition of the current in the circuit in which the device is connected. If overcurrents or fault currents occur which exceed some minimum value, but which are less than a maximum value, the interrupting capability of an interrupting unit of the device being within this range, the device is operating to interrupt the circuit. Fault currents or overcurrents in excess of the maximum value are not interrupted by the circuit interrupting device of that application, which in that event opens only after an upstream circuit breakers or similar device has interrupted the circuit.
The operating mechanism of the incorporated patent application is disclosed as usable with an interrupting unit having a pair of normally engaged, current-carrying contacts. The contacts are separable in an interrupting medium to interrupt the circuit. The operating mechanism includes a stored-energy operator and a tripping mechanism which selectively (1) prevent release of the stored energy to keep the contacts engaged, and (2) permit release of the stored energy to separate the contacts. The tripping mechanism includes a high mechanical advantage lever-link system which latches the stored energy when a low latching force is applied to the system. Also included is a movable member which in moving in a first direction stores energy capable of removing the low latching force, but otherwise leaves unaffected such low latching force. The member moves in a second direction solely under the influence of the stored latching-force-removing energy. A ratchet removes the low latching force from the lever-link system only when the movable member moves in the second direction.
The present invention relates to the minor modification or addition to the operating mechanism of the incorporated patent application, as well as to a novel shunt trip mechanism which is compatible with that operating mechanism and which furthers the ends and objects of the prior application, providing a simple, reliable, low-cost interrupting device, wherein fault interrupting ability is achieved at low cost.
As noted above, the prior application involves an operating mechanism for a circuit interrupting device. As used in this application, the term "operating mechanism" means a stored energy operator which selectively latches and releases stored energy in response to sensors which detect the condition of the current in circuit to which the circuit interrupting device is connected. Such operating mechanism and its intelligence is at line or bus potential. As used in this application, the term "shunt trip mechanism" refers to a mechanism at ground potential which is connected to or interacts with, the operating mechanism to operate the circuit interrupting device in response to any one of a number of conditions such as overpressure in a transformer, ground faults, or undesirable differential current condition in the transformer. Additionally, the shunt trip mechanism may be operated in response to a simple switch closure or push button operation for interruption of the circuit for any reason such as maintenance, repair, or inspection. As these two defined terms are used in this patent application, their ability to operate the circuit interrupting device is independent. Specifically, the operating mechanism has the ability of operating the circuit interrupting device, as described above, in response to overcurrents or fault currents within its operating capability, regardless of the condition of the shunt trip mechanism. Contrariwise, the shunt trip mechanism has the ability of operating the circuit interrupting device via the operating mechanism regardless of the current condition in the circuit to which the device is connected.